import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        int n=scanner.nextInt();
        feb(n);
        System.out.println(feb(n));
    }
    public static int feb(int n) {
        if (n < 1) {
            return 0;
        }
        if (n < 3) {
            return 1;
        } else {
            return feb(n - 1) + feb(n - 2);
        }
    }
}
